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WO1994011953A9 - Systeme d'elimination active du bruit - Google Patents

Systeme d'elimination active du bruit

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Publication number
WO1994011953A9
WO1994011953A9 PCT/US1993/010958 US9310958W WO9411953A9 WO 1994011953 A9 WO1994011953 A9 WO 1994011953A9 US 9310958 W US9310958 W US 9310958W WO 9411953 A9 WO9411953 A9 WO 9411953A9
Authority
WO
WIPO (PCT)
Prior art keywords
signal
bilateral transducer
transducer
bilateral
reverse output
Prior art date
Application number
PCT/US1993/010958
Other languages
English (en)
Other versions
WO1994011953A2 (fr
WO1994011953A3 (fr
Filing date
Publication date
Application filed filed Critical
Priority to AU62952/94A priority Critical patent/AU6295294A/en
Priority to US08/446,589 priority patent/US5862234A/en
Publication of WO1994011953A2 publication Critical patent/WO1994011953A2/fr
Publication of WO1994011953A3 publication Critical patent/WO1994011953A3/fr
Publication of WO1994011953A9 publication Critical patent/WO1994011953A9/fr

Links

Definitions

  • This invention relates in general to active noise cancellation systems, and in particular to such systems which employ a microphone proximate a listener's ear to receive essentially the same ambient noise received by the ear and a speaker for producing sound in the vicinity of the microphone to cancel the ambient noise.
  • An object of this invention is to provide the means to implement active noise attenuation systems without the need to use a microphone.
  • a further object of this invention is to provide an active noise attenuation system in a which a speaker is used as a bilateral transducer, i.e. a transducer that both converts acoustic waves to corresponding electrical energy and converts electrical energy to acoustic waves.
  • an improvement for at least eliminating the microphone from any ANC (“active noise control”) device having at least a microphone which responds to ambient acoustic noise waves and a speaker which transmits an altered version of the ambient noise waves over a frequency range to provide a measure of noise cancellation in the region of the microphone, the improvement comprising: (a) bilateral transducer means, disposed in said region, for converting the acoustic noise waves to a corresponding first signal and for converting a second signal to corresponding acoustic waves; and (>b) means ⁇ for applying a transfer function to-the first signal-,, over said frequency range, resulting in the second signal, the transfer function causing acoustic waves produced by the bilateral transducer to be generally equal in magnitude but opposite in phase to the acoustic noise waves impinging the bilateral transducer.
  • a first embodiment comprises: (a) a bilateral transducer means, disposed proximate a listener so as to be impinged by the same acoustic noise waves to which the listener is subjected, for converting the acoustic noise waves to a corresponding first signal and for converting a second signal to corresponding acoustic waves; and (b) means for applying a transfer function to the first signal, over a frequency range, resulting in the second signal, the transfer function causing acoustic waves produced by the bilateral transducer to be generally equal in magnitude but opposite in phase to the acoustic noise waves impinging the bilateral transducer.
  • a second embodiment comprising: (a) bilateral transducer means, disposed proximate a listener so as to be impinged by the same acoustic noise waves to which the listener is subjected, for converting the acoustic noise waves to a corresponding first signal and for converting a sum signal to corresponding acoustic waves; (b) means for applying a transfer function to the first signal, over a frequency range, resulting in a second signal; (c) a feed forward circuit comprising: (i) acousto-electric transducer means, disposed to be impinged by the same acoustic noise waves to which the listener is subjected for converting the noise waves to a corresponding third signal, and (ii) means for applying a transfer function to the third signal resulting in a fourth signal; and (d) means for summing the second and the fourth signals to produce the sum signal, the overall transfer function being ideally negative unity over the frequency range.
  • the drive to a speaker is periodically turned off at a rate above the hearing frequency limit, and in the "off period" the., speaker drive element is. sensed by .a circuit that produces a signal which is the combination of a signal representing the speaker velocity caused by a speaker drive signal and a signal caused by ambient noise because of the speaker's inherent ability to act as a microphone.
  • the latter signal is separated from the composite to produce a simulated microphone representation of ambient noise which is then processed in further active noise circuitry in a known ways.
  • Figure 1 is a functional block diagram of a prior art active noise cancellation system.
  • Figure 2 is a functional block diagram of a first embodiment of an active noise cancellation system according to this invention.
  • Figure 3 is a functional block diagram of a second embodiment of an active noise cancellation system according to this invention.
  • Figure 4 is a functional block diagram of a first embodiment of a bilateral transducer circuit according to this invention.
  • Figure 5 is a functional block diagram of a second embodiment of a bilateral transducer circuit according to this invention.
  • Figure 6 is a functional block diagram of a third embodiment of a bilateral transducer circuit according to this invention.
  • a basic prior art ANC system is illustrated to have a first transducer 2 in the form of a microphone proximate a listener's ear 4, e.g. inside of an earpiece covering the listener's ear.
  • the microphone is located to receive essentially the same acoustic noise that the ear is receiving and convert this noise into corresponding electrical energy, i.e. electrical signals at the microphone's output 6.
  • These electrical signals are processed by a signal processor 8 to produce speaker drive input signals 10 which are communicated to a speaker driver 12 which in turn sends corresponding electrical drive energy to a second transducer in the form of a speaker 14.
  • the speaker converts the electrical drive energy into corresponding acoustic waves which are directed to impinge the listener's ear.
  • the gain in the feedback loop is negative unity such that the acoustic waves impinging the ear from the speaker is at all times equal in magnitude but opposite in phase to that of the ambient noise impinging the ear.
  • the noise and the acoustic waves produced by the speaker are ideally summed to zero at the listener's ear.
  • a first embodiment of this invention is illustrated as having the microphone and speaker of Figure 1 replaced by a circuit 16 ("bilateral transducer circuit") having a bilateral transducer.
  • bilateral transducer shall refer to and mean a transducer which produces acoustic waves by means of a vibratory element in response to, and corresponding to, an energization signal applied to the transducer, and which produces a reverse output in response to, and corresponding to, mechanical movement of the vibratory element not attributable to energization.
  • the bilateral transducer is a speaker 18 disposed in the system to function both as a microphone and a speaker.
  • the bilateral transducer circuit produces a "microphone" output signal 20, a simulated microphone signal, corresponding to ambient noise.
  • the simulated microphone output signal is communicated to a signal processor 22 to produce a corresponding- speaker drive , input.- signal t .24,,, which,» is communicated to a speaker driver 26.
  • the speaker driver produces a corresponding speaker drive signal 28 which causes the bilateral transducer 18 to produce corresponding acoustic waves intended to cancel the ambient noise.
  • the loop gain is preferably negative unity.
  • a second embodiment of this invention is similar to the first embodiment illustrated in Figure 2 in that there exists an acoustic feedback loop utilizing a bilateral transducer circuit 30, but in addition there is a feed forward circuit having a microphone 32 which can be disposed inside or outside of an earpiece (not shown) the output of which is communicated to a first signal processor 34 the output of which is communicated as an input to a signal adder 36.
  • a signal adder 36 Another input to the adder is the output 38 of a second signal processor 40 which receives as an input a simulated microphone output 42 from the bilateral circuit 30.
  • the sum output of the adder is communicated to the bilateral circuit 30 as a speaker input drive signal 44.
  • Such a feed forward circuit is described in PCT Patent Application No.
  • a first embodiment of a bilateral transducer circuit is illustrated to have a speaker drive input signal 46A from an ANC system (e.g. see 24 and 44 of Figures 2 and 3) communicated to both a speaker drive circuit 48A and a speaker velocity synthesis circuit 50.
  • the speaker drive circuit contains an output stage 52A which produces a speaker drive signal 54A corresponding to the speaker drive input signal.
  • the speaker drive signal is communicated to a speaker 56A in order to cause it to produce acoustic waves intended to cancel ambient noise, but the speaker drive signal is gated "on” and “off” by a "Q" output of an oscillating chopper circuit 58.
  • e- ' chopper also provides a sampling clock 60 to a waveform sampling circuit 62 having an input communicating with the input of the speaker.
  • the sampling clock can be, or be derived from, for example the logical compliment of Q.
  • the output 64 of the waveform sampling circuit is communicated to a waveform reconstruction circuit 66, the output of which is communicated to a signal subtractor 68 which subtracts therefrom the output 70 of the speaker velocity synthesis circuit 50 to produce a simulated microphone output 72A for use in an ANC system (e.g. see 20 and 42 of Figures 2 and 3) .
  • the bilateral transducers can be diaphragm speakers with coil drives of conventional design because it is well known that they generate electrical energy corresponding and in response to mechanical movement of the diaphragms by external forces, such as ambient acoustic waves.
  • the bilateral transducers can be piezofilm transducers which basically are each a diaphragm coated with capacitive electrodes that can be made to bend or vibrate by input of electrical signals.
  • a piezofilm transducer is inherently bilateral in that if the diaphragm is bent or stretched as in vibration, it generates an output voltage.
  • the chopper circuit 58 preferably oscillates at a high frequency relative to audible sound, for example 100 kilohertz, which is sufficiently above the audible sound range to negligibly effect the noise cancellation.
  • the electrical energy generated by the speaker corresponds to the speaker's diaphragm velocity which is. the algebraic . sum of a velocity component caused by the speaker drive signal just gated off plus any velocity component due to impinging acoustic noise waves.
  • the waveform sampling circuit 62 samples the speaker's reverse output in response to each sampling clock and communicates the samples in real time to the waveform reconstruction circuit 66 which can be a low pass filter.
  • the output of the reconstruction circuit is a signal which corresponds in real time to the algebraic sum of the two diaphragm velocity components.
  • the reverse output signal also corresponds to the algebraic sum of the acoustic waves being created by the diaphragm due to the drive signal 54A and the acoustic noise waves impinging the diaphragm.
  • the speaker velocity synthesis circuit 50 produces a frequency dependent signal 70 corresponding to what the speaker's velocity response would be to the speaker drive input signal 46A without any external noise components, and therefore also corresponding to the acoustic waves being created by the diaphragm.
  • the simulated microphone output 72A is ideally a signal which corresponds only to the acoustic noise impinging the speaker's diaphragm.
  • a second embodiment of a bilateral transducer circuit is illustrated to have a speaker output stage 52B which receives as an input a speaker drive input signal 46B from an .ANC system (e.g. see 24 and 44 of Figures 2 and 3) .
  • the output stage produces a speaker drive signal 54B corresponding to the speaker drive input signal.
  • the speaker drive signal is communicated to a speaker 56B in order to cause it to produce acoustic waves intended to cancel ambient noise.
  • a sensing circuit 74 continuously senses the level of current in the signal path between the output stage and the speaker and produces a signal 76 ("current level signal”) corresponding thereto.
  • the sensing circuit can, for example, be a linear circuit having a differential input of relatively high impedance (so as not to unduly load the signal path) connected across the output impedance of the output stage.
  • the current in the signal path at any given time is the algebraic sum -of the current of the speaker drive signal 54B and the speaker's reverse output current, and therefore the current level signal corresponds in real time to the algebraic sum of the diaphragm velocity component caused by the speaker drive signal 54B and the velocity component due to impinging acoustic noise waves.
  • the speaker's velocity response to the speaker drive input signal 46B is synthesized in real time by a circuit 78 which produces a synthesized velocity signal 80 which is subtracted from the current level signal by a subtractor 82 to produce the simulated microphone output 72B for use in an ANC system (e.g. see 20 and 42 of Figures 2 and 3) .
  • the simulated microphone output 72A is ideally a signal which corresponds only to the acoustic noise impinging the speaker's diaphragm.
  • a third embodiment of a bilateral transducer circuit is illustrated to have a speaker output stage 52C which receives as an input a speaker drive input signal 46C from an ANC system (e.g. see 24 and 44 of Figures 2 and 3) .
  • the output stage produces a speaker drive signal 54C corresponding to the speaker drive input signal .
  • the speaker drive signal is communicated to a speaker 56C in order to cause it to produce acoustic waves intended to cancel ambient noise.
  • the speaker has a drive coil of conventional design but also has a sensing coil wound along therewith (not shown) for providing a speaker reverse output signal 84 ("sensing coil signal") that is dependent on the speaker diaphragm velocity and inductive coupling between the speaker drive coil (not shown) and the sensing coil .
  • a signal 86 produced by a speaker inductance synthesizing circuit 88 is subtracted from the sensing coil signal by means of subtractor 90.
  • the speaker inductance synthesizer is responsive to the speaker drive input signal 46C and the signal produced thereby simulates the signal induced in the sensing coil by the speaker drive coil.
  • the speaker's velocity response is synthesized- by a circuit 92 that produces a synthesized signal 94 that is also subtracted from the sensing coil signal by subtractor 90 to finally arrive at a simulated microphone signal 72C which ideally corresponds only to the acoustic noise impinging the speaker's diaphragm.
  • Each of the speaker velocity synthesizers described above can be an implementation of a transfer function based on a known model of the speaker.
  • the speakers of this invention can be modeled by known techniques. For example, a speaker can be characterized by applying known drive signals, within a selected frequency band, to the speaker's drive element while measuring the diaphragm's velocity. Preferably the known drive signals are random signals simulating noise over the frequency band in order to more accurately model the speaker for noise cancellation. From this the transfer function of the speaker can be determined and a synthesizer (e.g. a network of gain and phase shifting elements) can be designed therefrom using conventional design techniques. Likewise the speaker inductance synthesizer 88 of Figure 6 can be designed and implemented in similar fashion.
  • a synthesizer e.g. a network of gain and phase shifting elements
  • the inductive coupling can be characterized by applying known drive signals, e.g. simulated random signals, within a selected frequency band, to the speaker's drive element while measuring the sensing coil signals.
  • the synthesizers can each be implemented in a long term adaptive circuit varied in near real time.
  • bilateral transducer circuits While two embodiments of ANC systems having bilateral transducer circuits were described, the use of the bilateral transducer circuits is not limited to these ANC embodiments, but rather a bilateral transducer circuit according to this
  • [TODPCT3K.12] invention can be used to improve any device having at least a microphone which responds to ambient acoustic noise waves and a speaker which transmits an altered version of the noise waves over a frequency range to provide a measure of noise cancellation in the region of the microphone.
  • One improvement is the elimination of the microphone.
  • Other improvements and advantages are that the use of a speaker in a bilateral sense, that is as both a speaker and a microphone,- first of all puts the sensing surface co-planar with the speaker, and secondly tends to inverse frequency characteristics of the speaker which helps to compensate for speaker resonances and other undesirable characteristics.

Abstract

Transducteur bilatéral (18), utilisable dans un système d'élimination active du bruit, peut à la fois détecter le bruit ambiant et produire des ondes acoustiques pour éliminer le bruit. L'interface électrique pour chaque circuit transducteur bilatéral est constituée d'un signal d'attaque de haut-parleur servant de signal d'entrée et un signal de microphone simulé servant de signal de sortie. Selon un premier mode de réalisation, le signal d'attaque du transducteur bilatéral s'interrompt périodiquement à une cadence inaudible et, dans la 'période d'arrêt', l'élément d'attaque du transducteur produit un signal de sortie inversé qui est diminué d'un signal synthétisé représentant la réponse en vitesse du haut-parleur au signal d'attaque, afin de produire le signal de microphone simulé. Selon d'autres modes de réalisation, le signal de sortie inversé est déduit par la détection de l'énergie émise en direction du transducteur afin de produire les ondes acoustiques, ou par une bobine séparée dans un transducteur attaqué par bobine.
PCT/US1993/010958 1992-11-11 1993-11-12 Systeme d'elimination active du bruit WO1994011953A2 (fr)

Priority Applications (2)

Application Number Priority Date Filing Date Title
AU62952/94A AU6295294A (en) 1992-11-11 1993-11-12 Active noise cancellation system
US08/446,589 US5862234A (en) 1992-11-11 1993-11-12 Active noise cancellation system

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
AUPL5792 1992-11-11
AUPL579292 1992-11-11

Publications (3)

Publication Number Publication Date
WO1994011953A2 WO1994011953A2 (fr) 1994-05-26
WO1994011953A3 WO1994011953A3 (fr) 1994-07-07
WO1994011953A9 true WO1994011953A9 (fr) 1994-08-18

Family

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Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/US1993/010958 WO1994011953A2 (fr) 1992-11-11 1993-11-12 Systeme d'elimination active du bruit

Country Status (1)

Country Link
WO (1) WO1994011953A2 (fr)

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* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5848169A (en) * 1994-10-06 1998-12-08 Duke University Feedback acoustic energy dissipating device with compensator
DE19735450C1 (de) * 1997-08-16 1999-03-11 Bosch Gmbh Robert Verfahren zur Eingabe von akustischen Signalen in ein elektrisches Gerät und elektrisches Gerät
US6717537B1 (en) * 2001-06-26 2004-04-06 Sonic Innovations, Inc. Method and apparatus for minimizing latency in digital signal processing systems
CN1768555A (zh) * 2003-04-08 2006-05-03 皇家飞利浦电子股份有限公司 用于减少麦克风信号中的干扰噪声信号部分的方法和装置
US20050136848A1 (en) * 2003-12-22 2005-06-23 Matt Murray Multi-mode audio processors and methods of operating the same
EP2384023A1 (fr) * 2010-04-28 2011-11-02 Nxp B.V. Utilisation de haut-parleur en tant que capteur de vibrations
EP2387251B1 (fr) * 2010-05-11 2013-07-17 Nxp B.V. Reproduction et détection sonore
CN114333755A (zh) * 2022-03-17 2022-04-12 滨州学院 一种汽车行驶中车内噪声的智能监测与降噪装置和方法

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GB2010639B (en) * 1977-12-14 1982-05-19 Matsushita Electric Ind Co Ltd Transducer
US4985925A (en) * 1988-06-24 1991-01-15 Sensor Electronics, Inc. Active noise reduction system
US5267321A (en) * 1991-11-19 1993-11-30 Edwin Langberg Active sound absorber

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